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Thu, 06 Sep 2018 03:22:39 -0700 (PDT) From: Minchan Kim To: Andrew Morton , linux@armlinux.org.uk Subject: [RFC 3/3] arm: mm: support get_user_pages_fast Date: Thu, 6 Sep 2018 19:22:12 +0900 Message-Id: <20180906102212.218294-4-minchan@kernel.org> X-Mailer: git-send-email 2.19.0.rc1.350.ge57e33dbd1-goog In-Reply-To: <20180906102212.218294-1-minchan@kernel.org> References: <20180906102212.218294-1-minchan@kernel.org> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20180906_032251_476555_358E5014 X-CRM114-Status: GOOD ( 17.90 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: steve.capper@linaro.org, catalin.marinas@arm.com, will.deacon@arm.com, linux-kernel@vger.kernel.org, Minchan Kim , android-treble-mediatek-ext@partner.android.com, kernel-team@android.com, linux-arm-kernel@lists.infradead.org Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Virus-Scanned: ClamAV using ClamSMTP Recently, there was a report get_user_pages_fast helps app launching speed due to reducing uninterruptible sleep time because we don't need to contend for mmap_sem, I believe. With get_user_pages_fast, that uniterruptible sleep time is reduced about 5~10% by testing. Cc: Russell King Cc: Catalin Marinas Cc: Will Deacon Cc: Steve Capper Signed-off-by: Minchan Kim --- arch/arm/mm/Makefile | 6 ++ arch/arm/mm/gup.c | 221 +++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 227 insertions(+) create mode 100644 arch/arm/mm/gup.c diff --git a/arch/arm/mm/Makefile b/arch/arm/mm/Makefile index 7cb1699fbfc4..f55f96d56843 100644 --- a/arch/arm/mm/Makefile +++ b/arch/arm/mm/Makefile @@ -13,6 +13,12 @@ obj-y += nommu.o obj-$(CONFIG_ARM_MPU) += pmsa-v7.o pmsa-v8.o endif +ifneq ($(CONFIG_ARM_LPAE),y) +ifeq ($(CONFIG_ARCH_HAS_PTE_SPECIAL),y) +obj-$(CONFIG_MMU) += gup.o +endif +endif + obj-$(CONFIG_ARM_PTDUMP_CORE) += dump.o obj-$(CONFIG_ARM_PTDUMP_DEBUGFS) += ptdump_debugfs.o obj-$(CONFIG_MODULES) += proc-syms.o diff --git a/arch/arm/mm/gup.c b/arch/arm/mm/gup.c new file mode 100644 index 000000000000..44e12fb7430e --- /dev/null +++ b/arch/arm/mm/gup.c @@ -0,0 +1,221 @@ +// SPDX-License-Identifier: GPL-2.0 +#include +#include +#include +#include + +static inline pte_t gup_get_pte(pte_t *ptep) +{ + return READ_ONCE(*ptep); +} + +static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, + int write, struct page **pages, int *nr) +{ + int ret = 0; + pte_t *ptep, *ptem; + + ptem = ptep = pte_offset_map(&pmd, addr); + do { + pte_t pte = gup_get_pte(ptep); + struct page *page; + + if (!pte_access_permitted(pte, write)) + goto pte_unmap; + + if (pte_special(pte)) + goto pte_unmap; + + VM_BUG_ON(!pfn_valid(pte_pfn(pte))); + page = pte_page(pte); + + if (!page_cache_get_speculative(page)) + goto pte_unmap; + + if (unlikely(pte_val(pte) != pte_val(*ptep))) { + put_page(page); + goto pte_unmap; + } + + SetPageReferenced(page); + pages[*nr] = page; + (*nr)++; + + } while (ptep++, addr += PAGE_SIZE, addr != end); + + ret = 1; + +pte_unmap: + pte_unmap(ptem); + return ret; +} + +static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end, + int write, struct page **pages, int *nr) +{ + unsigned long next; + pmd_t *pmdp; + + pmdp = pmd_offset(&pud, addr); + do { + pmd_t pmd = READ_ONCE(*pmdp); + + next = pmd_addr_end(addr, end); + if (!pmd_present(pmd)) + return 0; + else if (!gup_pte_range(pmd, addr, next, write, pages, nr)) + return 0; + } while (pmdp++, addr = next, addr != end); + + return 1; +} + +static int gup_pud_range(p4d_t *p4dp, unsigned long addr, unsigned long end, + int write, struct page **pages, int *nr) +{ + unsigned long next; + pud_t *pudp; + + pudp = pud_offset(p4dp, addr); + do { + pud_t pud = READ_ONCE(*pudp); + + next = pud_addr_end(addr, end); + if (pud_none(pud)) + return 0; + else if (!gup_pmd_range(pud, addr, next, write, pages, nr)) + return 0; + } while (pudp++, addr = next, addr != end); + + return 1; +} + +static int gup_p4d_range(pgd_t *pgdp, unsigned long addr, unsigned long end, + int write, struct page **pages, int *nr) +{ + unsigned long next; + p4d_t *p4dp; + + p4dp = p4d_offset(pgdp, addr); + do { + next = p4d_addr_end(addr, end); + if (p4d_none(*p4dp)) { + return 0; + } else if (!gup_pud_range(p4dp, addr, next, write, pages, nr)) + return 0; + } while (p4dp++, addr = next, addr != end); + + return 1; +} + + +static void gup_pgd_range(unsigned long addr, unsigned long end, + int write, struct page **pages, int *nr) +{ + unsigned long next; + pgd_t *pgdp; + + pgdp = pgd_offset(current->mm, addr); + do { + next = pgd_addr_end(addr, end); + if (pgd_none(*pgdp)) + return; + else if (!gup_p4d_range(pgdp, addr, next, write, pages, nr)) + break; + } while (pgdp++, addr = next, addr != end); +} + +bool gup_fast_permitted(unsigned long start, int nr_pages, int write) +{ + unsigned long len, end; + + len = (unsigned long) nr_pages << PAGE_SHIFT; + end = start + len; + return end >= start; +} + +/* + * Like get_user_pages_fast() except its IRQ-safe in that it won't fall + * back to the regular GUP. + */ +int __get_user_pages_fast(unsigned long start, int nr_pages, int write, + struct page **pages) +{ + unsigned long addr, len, end; + unsigned long flags; + int nr = 0; + + start &= PAGE_MASK; + addr = start; + len = (unsigned long) nr_pages << PAGE_SHIFT; + end = start + len; + + if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ, + (void __user *)start, len))) + return 0; + + /* + * Disable interrupts. We use the nested form as we can already have + * interrupts disabled by get_futex_key. + * + * With interrupts disabled, we block page table pages from being + * freed from under us. See mmu_gather_tlb in asm-generic/tlb.h + * for more details. + * + * We do not adopt an rcu_read_lock(.) here as we also want to + * block IPIs that come from THPs splitting. + */ + + if (gup_fast_permitted(start, nr_pages, write)) { + local_irq_save(flags); + gup_pgd_range(addr, end, write, pages, &nr); + local_irq_restore(flags); + } + + return nr; +} + +int get_user_pages_fast(unsigned long start, int nr_pages, int write, + struct page **pages) +{ + unsigned long addr, len, end; + int nr = 0, ret = 0; + + start &= PAGE_MASK; + addr = start; + len = (unsigned long) nr_pages << PAGE_SHIFT; + end = start + len; + + if (nr_pages <= 0) + return 0; + + if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ, + (void __user *)start, len))) + return -EFAULT; + + if (gup_fast_permitted(start, nr_pages, write)) { + local_irq_disable(); + gup_pgd_range(addr, end, write, pages, &nr); + local_irq_enable(); + ret = nr; + } + + if (nr < nr_pages) { + /* Try to get the remaining pages with get_user_pages */ + start += nr << PAGE_SHIFT; + pages += nr; + + ret = get_user_pages_unlocked(start, nr_pages - nr, pages, + write ? FOLL_WRITE : 0); + + /* Have to be a bit careful with return values */ + if (nr > 0) { + if (ret < 0) + ret = nr; + else + ret += nr; + } + } + + return ret; +}